meta-nuvoton: update Yocto compat for gatesgarth

The next release of Yocto is soon and most of the upstream
layers have switched support strings for it.  Support layer
compat for gatesgarth (current) and dunsfell (previous).

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Iad57d8d70141b449fa9d98408a2f139946770e87
diff --git a/conf/layer.conf b/conf/layer.conf
index 19af7e9..eaf9a52 100644
--- a/conf/layer.conf
+++ b/conf/layer.conf
@@ -7,4 +7,4 @@
 BBFILE_COLLECTIONS += "nuvoton-layer"
 BBFILE_PATTERN_nuvoton-layer = ""
 LAYERVERSION_nuvoton-layer = "1"
-LAYERSERIES_COMPAT_nuvoton-layer = "warrior zeus dunfell"
+LAYERSERIES_COMPAT_nuvoton-layer = "dunfell gatesgarth"